Overheating after Impeller Replacement

[bruceb58]

If boat engine is normal, you've eliminated heat exchanger and exhaust.

I haven't heard him mention a heat exchanger once. I am assuming he has a raw water cooled engine.

 

[ed_hall1]

You do not want to do that. The water needs to be at the level of the impeller on the front of the engine and there is no way you are getting it to that level with a trough.

With the engine on muffs and running, pull the hoses one at a time that go from the thermostat housing to the exhaust manifold and see what type of water flow you are getting. The outlets of the thermostat housing can get corroded and limit water flow.

You are running the water to your muffs at full water pressure right?

Good point. I will stay with the muffs.

Also, the engine is raw water cooled.

 

[dennis461]

No Title

I stopped using muffs on my drive a few years ago.
Too much hassle trying to seal.
If your system is working correctly(which is the main reason for my running in the driveway)
The raw water pump with a little priming will draw a vacuum and pull water up .
I fill my drum up to the cavitation plates.

Now, some other forum members may not like this method, but, if my boat has an air leak, or worn impeller, or partially blocked heat exchanger or manifold, then I won't get water flow in my sight glass, and I know right away I have a problem.

I just have to remember to add cold water after about 5-10 minutes :-0

 

[bruceb58]

The raw water pump with a little priming will draw a vacuum and pull water up

It is not designed to draw water up hence the reason it's mounted below the water line.

Great way of burning up the impeller.

 

[dennis461]

It is not designed to draw water up hence the reason it's mounted below the water line.

Great way of burning up the impeller.

Breeuce , you are wrong.
When on plane, everything is above the water line except part of my outdrive.
, by your response, I would burn up an impeller everytimg my boat lifted out of the water.

Do you own a 270 or 280 drive?

So is there some magic going on in my driveway?
My boat draws water from a barrel with no problems if all connections are tight.

 

[spoilsofwar]

When on plane, (and any time when the boat is actually moving) the forward motion of your drive thru the water creates pressure which forces water up onto the drive. Have you accounted for that in your theory?

Bruce is not wrong. The engine mounted pump is not designed to create a suction and draw water uphill. That's why it is below water level when the boat is in the water.

Also not sure why you are asking about a 270/280 drive. The OP's boat is much newer and by his original post is equipped with a DP series drive.

 

[dennis461]

When on plane, (and any time when the boat is actually moving) the forward motion of your drive thru the water creates pressure which forces water up onto the drive. Have you accounted for that in your theory?.

Of course, but if you do the math there is very little pressure gains as the intake is on the side of the drive not the front, so V^2 must be reduced by side slip de-pressureiation.(Which is why I ran the PVC to take advantage of the direct frontal intake)

Millions of people use a drum instead of muffs.

That's why it is below water level when the boat is in the water.

If there was no suction(air vacuum), then all boats would need the RWP primed...
These are positive displacement pumps, not centrifugal pumps.

Did you guys look at my picture? It works everytime, you are wrong.
Should I post a video?

edhall1, if the new raw water pump does not cure the problem, send me a PM.

 

[bruceb58]

Yep...up on plane water is forced into the drive. The water intake on the side of the SX drive that I have has recesses right before the input holes hence forcing the water into the holes.

Millions of people use drums who have I/O drives or outboards with water impellers in the drive. That is fine if you have a Merc Alpha since the impeller is now under the water. If you use a Merc Bravo, it is not ok.

I have a Volvo SX currently just like the OP of this thread. I also used to own a Volvo 270 and it has a water pickup on the nose of the drive just for the purpose of forcing water when on plane!

I have no doubt your pump eventually sucks the water out of your drum....only after being dry for awhile. Not good for the impeller.

And sorry, but having a piece of PVC pipe hanging in the water as a pickup is 'mickey mouse" and just asking for your engine to overheat when that thing breaks off.

 

[Maclin]

dennis461 Regarding up on plane, your boat does not just drop into the water, engine running, at 40mph on plane. When actually in the water, the boat starts out still, water level is way up onto the drive and the pump in the front can prime easily, and maintain that prime even up on plane. On the trailer the drive prevents the tub from being able to submerge the drive to the same level as if in the water. The pump in the front may not be able to prime at all. If there is water already in the lines to the front pump then a slight goose on the throttle may produce the prime and water flows ok. Dry lines, and the prime is very iffy. The VP DPA unit I had would keep the water in the lines and the impeller would more or less be "submerged" and could prime quickly from a tub the next time. But totally dry, and if you just have to run in a tub, best to use muffs first and prime the lines, then put in a tub. Keep fresh water going into the tub. And if you are running one of the older white 270/80/90/DPA drives plug that bottom drain hole when using the muffs.

 

[dennis461]

As i said in my post, I prime the RWP, every time, on the water, off the water. Get the rubber lubed up first. I have never had to replace an impeller due to damage (knock on wood). I've been using my bucket method in the driveway for over four years., beginning of season, end of season, couple times mid season if needed, and in winter.

I open the strainer and pour about one quart of water in.
Most of it fills the inlet copper tube, some goes 'upstream' to heat exchanger.
Now the fun starts.
I walk 6 feet to the helm and hit the starter.
Quickly walk back to strainer and put the strainer lid back on as water fills the system.
If I drop the lid or work too slow., the strainer overflows.
So my method works.

Why are you doubting it?

I posted some years ago a third alternative which you may more pleased with...
Eliminates the poor fitting muffs, and uses 1/2 hole to put water into drive.
As I say in the video, duct tape over the inlet ports (not too tightly).
Shove a hose up the 1/2 hole.
Use low volume of water from garden hose.
https://www.youtube.com/watch?v=B2gcD78z64I

Now if there is a vacuum leak on the inlet portion of the system,
I think the muffs method will hide it.
I know how the RWP vacuum outdrive system works, Any Volvo, rubber pump, engine mounted will have the same principle., the pump 'pull's vs 'pushes'

The OP can use whatever method he chooses.

Since he seems to have eliminated most problems, he either has a worn RWP casing/cover, or a vacuum leak in the leg.

 

[bruceb58]

LOL.....I think I will skip all those steps thank you very much.

The OP has an SX with a V8. He does not have a strainer. He does not have a heat exchanger. The pump primes by itself since the RWP sits below the water line.

Muffs work great. You use high HIGH volume from the hose...not low. SX drives don't have issues with vacuum leaks like the 270 typically can have with the elbow corroding on the top of the drive. Even if an SX did have a vacuum leak, you would never see it at idle since everything that would leak is under water and on plane you have positive pressure form the water entering the drive.

I am curious...have you ever even owned an SX or taken the drive off of one? Have you ever seen how the raw water line runs from the drive to the water pump?

These are the best style muffs. Delivers water on both sides.
https://smile.amazon.com/Marine-FLUS...flushing+drive

 

[bruceb58]

To the OP...use a clear section of hose between the thermostat and the hose feeding it. Will tell you if you have air entering somewhere like your pump. This is a Volvo recommended trouble shooting step.

 

[dennis461]

OP, if still struggling this Memorial Day weekend read through these threads...
Double o-ring problem or
plastic insert problem

http://forums.iboats.com/forum/engi...mp-wont-prime-probably-simple-any-ideas/page2

similar problems
http://www.marineengine.com/boat-forum/showthread.php?384397-Volvo-Penta-not-pumping-water

t-line fitting instead of muffs
http://www.offshoreonly.com/forums/...aw-water-impeller-now-difficulty-priming.html

 

[ed_hall1]

No Title

Still frustrated?but hopefully getting closer to the real issue/s.
Here?s the latest.

1. I installed a new impeller outer housing with no improvement (Volvo part # 3858115). The original back plate on the impeller housing did have some minor black streaks. I am not sure if my previously failed impeller may have damaged or grooved the impeller plate and that is now causing the impeller to not seal properly and therefore causing issues. I will have to check for straightness and grooving tonight (as dennis461 has suggested here).
2. I did remove the impeller hose and added a 3? clear hose to the impeller inlet. I then shot water (under pressure) to the raw water pump. The impeller took the water and distributed it correctly to the engine and out the risers. No overheating, but probably not a fair test for the impeller as the water was under pressure.
3. I also held my muffs tightly against the out drive and got very minimum water flow at the impeller with the hoses removed. If I stopped applying pressure to the muffs all water flow to the impeller stopped. I did also shot water from the impeller inlet hose out the out drive and got great flow. Question. Could I be getting a one way restriction in water flow from my out drive to the impeller???? Should I get water flow at the impeller when the muffs are on?

Thanks to all the responses and sticking with me through all my tests thus far.

 

[Jeepster04]

If you forced water to the impeller and it worked as it should then it sounds like youre narrowing things down. You need to run the boat at the lake with the 3' clear hose in place and see if it is pulling water from the lake. If its not, you have some sort of vacuum leak which is allowing air into the system. You will be able to see the air in the clear hose. That will really let you knows whats happening.

Ive not checked/read everything so forgive me, but have you tried the old impeller/verified that you have the correct impeller? We bought the wrong impeller a few years back and it caused overheating issues. Only after putting the clear hose directly into the lake did I figure that issue out. It wasnt pulling any water! Put the old impellers in and boom, all was well. Ive never tried using muff's on our SX-A since it has the hose hookup right by the engine. Thats always worked greeeeeat.

And just for the record, the raw water pump had no issues pulling the water up and over the side of the boat out of the lake.. It was actually... pulling... the water... up....

 

[bruceb58]

Question. Could I be getting a one way restriction in water flow from my out drive to the impeller???? Should I get water flow at the impeller when the muffs are on?

There is one thing between the drive and the pump and that is the power steering cooler. It might be worth checking that out.

 

[dypcdiver]

I have to agree with bruceb58, Pull the hose off the Power steering cooler and check for blockage, I know it is restricted access, try using a phone to take a picture if you cannot get your head in there. https://www.volvopentashop.com/Vols...7478_033?path=MarineGasolineEngines/7797478%2 F7797478_64%2F7797478_033
Check the hoses No. 23 & 6 have not collapsed internally.
I am assuming that you have checked that the inlet holes on the outdrive leg are clear of marine growth or sand if you have ever touched bottom.

 

[ed_hall1]

Update. Issue finally resolved last night!!!!!!!!!!

I received and installed my new Volvo raw-water pump last night. This was the complete assembly with pulley, bearing, impeller and housing all assembled and tested at the factory (not cheap). It appears that my original raw-water pump's inner bearing seal was the issue. Although it never leaked a drop of water, the seal would suck air when the impeller was spinning and under load. This introduced air into the system and therefore did not allow sufficient water to be sucked from the out-drive and properly cool the engine. When I installed the new pump and started the engine, I had water shooting vertically at least five inches high at the thermostat housing connection (with the hose disconnected). With the muffs on and the engine running, the muffs leaked very little water and were sucked tightly to out-drive. Before the replacement the muffs were spraying water everywhere as if the engine was not even running.

Note to myself and anyone else replacing the impeller: You may want to consider using a "Volvo-Penta Raw Water Rebuild Kit" if you are not getting a nice column of water at the thermostat housing. A little more work to replace the bearing, seal and impeller, but definitely worth the improved cooling and water flow.

Thank you to everyone for all their insights and post!!!